Generic access network (GAN) protocols and operations allow a properly configured wireless communication device to maintain voice call continuity (VCC) as it moves between cellular coverage and local, unlicensed wireless coverage. With GAN capability, users can place voice (and data) calls using a cellular communication network and have call traffic shifted to the potentially cheaper and faster service offered by a Wireless LAN (WLAN) or essentially any other network, system, or access point that offers an Internet Protocol (IP) bearer. For example, a mobile operator providing cellular communication services via a GSM/GPRS network can extend coverage to WLANs or other IP-based networks by coupling them to the GSM/GPRS core network through an appropriately configured network controller.
In the context of GSM/GPRS, GAN protocols and operations are specified by the Third Generation Partnership Project (3GPP) Technical Specifications 43.318 and 44.318. The addition of GAN technology to existing GSM/GPRS networks enables users to roam seamlessly between the wide area GSM/GPRS network and local area networks having IP connectivity to the GSM/GPRS network. WiFi (802.11 b/g/n) radio transceivers are thus commonly included in GAN-enabled cellular handsets.
When a local network is detected by such a handset, it establishes a secure IP connection through a gateway to a server called a GAN Controller (GANC) that is owned or otherwise associated with the mobile operator. The GANC communicatively couples to the GSM/GPRS core network of the mobile operator and makes the signaling coming from the handset look like it is coming from another base station in the GSM/GPRS network. The GANC thus appears to be just another base station from the core network's perspective, although mobility management obviously is different, as the GANC can provide support for devices in any number of geographically separated wireless hotspots.
With the above in mind, GAN technology may be understood as replacing the radio connection between a cellular terminal and a supporting cellular network with an IP connection provided through a local access network. Supporting such operation, GAN functionality broadly divides into three tightly connected main parts: the (cellular) network signaling for access, authentication, and call processing; IP connection control signaling for establishing and carrying out IP-based communications; and, at least for Voice-over-IP (VoIP) calls, audio system processing for handling audio data stream coding/decoding and executing associated audio algorithms.